Current analysis devices, as are routinely used in analytics, forensics, microbiology and clinical diagnostics, are able to carry out a multiplicity of detection reactions and analyses with a multiplicity of samples. In order to be able to carry out a multiplicity of examinations in an automated manner, various automatically operating apparatuses for the spatial transfer of measurement cells, reaction containers and reagent liquid containers are required, such as, e.g., transfer arms with gripper functions, transport belts or rotatable transport wheels, as well as apparatuses for transferring liquids, such as, e.g., pipetting apparatuses. The devices comprise a central control unit which, by means of appropriate software, is able to largely autonomously plan and work through the work steps for the desired analyses.
Many of the analysis methods used in such analysis devices operating in an automated manner are based on optical methods. Measurement systems based on photometric (e.g. turbidimetric, nephelometric, fluorometric or luminometric) or radiometric measurement principles are particularly widespread. These methods enable the qualitative and quantitative detection of analytes in liquid samples without having to provide additional separation steps. The determination of clinically relevant parameters, such as, e.g., the concentration or the activity of an analyte, is often implemented by virtue of an aliquot of a bodily fluid of a patient being mixed simultaneously or in succession with one or more test reagents in a reaction vessel, as a result of which a biochemical reaction is put into motion, which brings about a measurable change in an optical property of the test preparation.
The measurement result is, in turn, forwarded into a storage unit by the measurement system and evaluated. Subsequently, the analysis device supplies a user with sample-specific measurement values by way of an output medium, such as, e.g., a monitor, a printer or a network connection.
Sample liquids or reagent liquids are usually transferred by means of automated pipetting apparatuses. Such pipetting apparatuses generally comprise a height-adjustable pipetting needle arranged vertically on a displaceable transfer arm, which pipetting needle is connected to a pumping unit such that a desired volume of liquid can be taken from a container by way of the pipetting needle, and output into a target container at a different location. Usually, the pipetting needle is displaced to a position over a liquid container with the aid of the transfer arm and then lowered into the liquid container and into the liquid contained therein. Once the desired volume has been withdrawn, the pipetting needle is driven upward and then driven to the desired target position over a liquid container, e.g., over a measurement cell, with the aid of the horizontally displaceable transfer arm. There, the pipetting needle is lowered again, and the amount of liquid is output.
It is conventional to equip pipetting apparatuses with a fill-level sensor. The purpose of this is, firstly, to be able to determine the fill level of reagent liquids in reagent liquid containers during the operation of the automated analysis device and report this to the control unit. What this ensures, for example, is that a user can be informed in good time about a necessary reagent container replacement. Secondly, determining the fill level ensures that the pipetting needle is always immersed sufficiently deeply into the liquid to be withdrawn in order to avoid air being suctioned-in in place of liquid.
The most common method for determining the fill level is the determination of the fill level by capacitive means. To this end, the pipetting needle consists of an electrically conductive material and hence, in principle, forms the measurement electrode, and it furthermore comprises a reference electrode. The fill level can be determined continuously from the change in the electric capacitance between the pipetting needle and the reference electrode. Determining the fill level by optical means is another method. To this end, the pipetting needle comprises an optoelectronic fill-level sensor consisting of a light source and a light sensor. In the case of immersion, the light is refracted by the liquid and it no longer reaches the light sensor, or it only reaches the latter in attenuated form. The fill level can be determined from the attenuation of the light signal.
The pipetting needle tips must be cleaned after each instance of pipetting sample or reagent liquid before they can be used for the processing of further reagents or samples. In an analysis device, special wash stations are provided for cleaning pipetting needle tips. Conventional wash stations are composed of an inner wash fountain cylinder, which is filled or fillable with a wash liquid, and an outer overflow cylinder. For cleaning purposes, the pipetting needle tip is lowered into the wash fountain cylinder and immersed into the wash liquid. In some systems, the wash liquid is sprayed into the wash fountain cylinder with a high flow velocity through nozzles in order to optimize the cleaning process. In some systems, wash liquid is suctioned-in and emitted again so that the interior of the pipetting needle tip is cleaned as well. In other systems, the pump apparatus of the pipetting apparatus comprises a direct supply of wash liquid such that the wash liquid is pumped through the whole pipetting needle and subsequently emitted into the wash fountain cylinder. The outer overflow cylinder surrounding the wash fountain cylinder is provided to collect wash liquid which passes over the edge of the wash fountain cylinder. A drain is usually provided in the overflow cylinder, by means of which the collected wash liquid can flow out of the wash station or can be suctioned therefrom. By way of example, such a wash station for a pipetting needle is described in WO-A1-97/03766.
A problem is that, for example, the drain can be blocked, as a result of which—in the worst case—the wash station overflows and wash liquid can reach into the analysis device and cause major damage as a result thereof. Other malfunctions, such as, e.g., uncontrolled filling with wash liquid or a failure of a suctioning apparatus, can also cause an overflow of a wash station.
It is therefore necessary to adopt measures which identify and indicate the risk of the overflow of a wash station in good time.